Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 121516
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1016 AM CDT Sat Aug 12 2017

.DISCUSSION...
Quick update...main issue today should be the heat. Heat index
readings of 103 to 108 should blanket the region. Heat advisory
focused over the SW half of the region where 105-108 H.I. should
prevail and other than to add two counties (Liberty/Montgomery)
where dewpoints should hold on a little longer into the early
afternoon hours yielding the needed 108 H.I. before rain chances
increase slightly will maintain the advisory. Rain chances should
be mainly focused along the seabreeze and isolated in nature and
more predominantly from NETX into LA with moisture pooled to the
southwest of the boundary. GOES 16 showing a plume of 2.0" PW
near/NE of DFW extending down to richer moisture around LCH of
2.3" clipping our northeast counties with 2" PW while SW portions
of SETX are much drier at 1.6-1.7" and likely far more capped.
Following the previous package with very low POPS near Columbus
increasing toward Groveton/Crockett. Will need to watch the
behavior of deep convection late this afternoon/evening across the
NTX area as some models swing an MCS southeastward and it could
clip the northeast portions of the area (Crockett to Livingston)
between midnight and noon. Tomorrow looking warmer than today
unfortunately and Heat Advisory may be needed again.

45

&&

.PREV DISCUSSION... /ISSUED 623 AM CDT Sat Aug 12 2017/

AVIATION...
A fairly strong upper level high pressure area will keep mainly
VFR conditions across Southeast Texas today and tonight. Very
widely scattered areas of patchy ground fog could impact KLBX or
KCXO before 14Z. Otherwise, there is a slight chance that
isolated showers will develop along the sea breeze and bay breeze
and affect mainly KIAH and KHOU during the late afternoon after
20Z. However, any showers that do develop are expected to diminish
by 00Z. A few of the models do have better chances for showers
and thunderstorms just north of KUTS later today and tonight. Do
not think these will work their way far enough southward to affect
the site.

40

PREV DISCUSSION... /ISSUED 404 AM CDT Sat Aug 12 2017/

DISCUSSION...
At 3 AM, a small area of showers was moving SE across Houston
County but for the most part the area remains dry with a cirrus
shield covering the region. Temperatures remain very warm with
many locations still in the lower 80`s. A warm start to the day
coupled with warm 850 mb temps should yield another hot day across
SE TX but am expecting some slightly drier air aloft to mix to
the surface today resulting in lower dew points and lower humidity
levels. We already have the Heat Advisory in effect so won`t drop
it but not convinced we`ll see widespread +108 heat index values.
At 850 mb, a trough of low pressure extended from an area of low
pressure over the Great lakes into North Texas. 850 mb moisture
looked plentiful from DFW to LCH. The combination of the trough
and the moisture should yield more clouds over the NE half of the
area and probably some scattered showers and storms. Will carry
some low PoPs over the extreme north tonight as yet another weak
upper level disturbance clips the area. Overnight temperatures
will once again be very warm and probably only briefly fall below
80 degrees around sunrise.

Sunday will again be warm and PW values lower to around 1.75
inches with weak capping noted in the 850-700 layer. 850 temps
support high temps in the upper 90`s yet again. There is more dry
air that should mix to the surface on Sunday so again heat index
values will be marginal for a Heat Advisory. Sunday night again
looks warm with temperatures briefly falling into the upper 70s.

850 temps are progged to cool a bit early next week and this
could possibly portend slightly cooler surface temps on Mon/Tues.
PW values briefly perk up to around 1.90 inches Monday and
Tuesday. Will maintain slight rain chances on Mon as PW values
increase and convective temps lower. Better rain chances possible
on Tuesday as convective temps fall further and 850 mb temps cool
and capping at 850 mb weakens.

The second half of next week looks quiet as upper level ridging
builds overhead. The ECMWF is more aggressive with moisture and
would suggest scattered afternoon showers while the GFS is drier.
Have blended PoPs between the two models for Wed-Fri. 500 mb
heights don`t look extreme starting out near 594 DM but eventually
lowering to around 590-592 DM which for August is not too bad.
Both models are suggesting near normal temperatures which seems
reasonable considering the modest 500 mb heights in place. 43

MARINE...
High pressure over the northern Gulf of Mexico will keep southerly
winds in place across the Upper Texas coastal waters through the
middle of the upcoming week. The pressure gradient caused by the
interaction between the surface high pressure area over the Gulf and
a low pressure system in the Southern plains will increase tonight
and Sunday. This will cause the winds to increase to caution
conditions for most areas mainly during the night time and early
morning hours from Sunday night through Wednesday night.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      99  78  98  77  99 /  10  10  10  10  10
Houston (IAH)              96  79  97  78  97 /  20  10  10  10  20
Galveston (GLS)            90  84  91  84  90 /  20  10  10  10  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 7 PM CDT this evening for the following
     zones: Austin...Brazoria...Brazos...Burleson...Chambers...
     Colorado...Fort Bend...Galveston...Grimes...Harris...
     Jackson...Liberty...Madison...Matagorda...Montgomery...
     Waller...Washington...Wharton.

GM...NONE.
&&

$$

Discussion...45



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